Kelly wrote:
> On Apr 21, 2:33 pm, Brent Meeker <meeke....domain.name.hidden> wrote:
>
>> These states can belong to more than one sequence of
>> conscious experience. But the question is whether the order of the
>> states in the computation is always the same as their order in any
>> sequence of conscious experience in which they appear? For example, if
>> there is a computation of states A, B, and C then is that a possible
>> sequence in consciousness? In general there will be another, different
>> computation that computes the states in the order A, C, B, so is that
>> too a possible sequence in consciousness?
>>
>
> Hypothetical situation, assuming an objectively existing physical
> universe. All of the particles in the universe kick into reverse and
> start going backwards. For some reason every particle in the universe
> instantaneously reverses course. And also space begins contracting
> instead of expanding. Everything in the universe hits a rubberwall and
> bounces back 180 degrees.
>
> So now instead of expanding, everything is on an exact "rewind" mode,
> and we're headed back to the "Big Bang".
>
> The laws of physics work the same in both directions...if you solve
> them forward in time, you can take your answers, reverse the equations
> and get your starting values, right? With the possible exception of
> kaon decay, but we'll leave that aside for now.
>
> This is what they always go on about with the "arrow of time". The
> laws of physics work the same forwards and backwards in time. It's not
> impossible for an egg to "unscramble", it's just very very very very
> very unlikely. But if it did so, no laws of physics would be broken.
> And, in fact, if you wait long enough, it will eventually happen.
>
> Okay, so everything has reversed direction. The actual reversal
> process is, of course, impossible. But after everything reverses,
> everything just plays out by the normal laws of physics. Only that one
> instant of reversal breaks the laws of physics.
>
> External time is still moving forward, in the same direction as
> before. We didn't reverse time. We just reversed the direction of
> every particle.
>
> So, now photons and neutrinos no longer shoot away from the sun -
> instead now they shoot towards the sun, which when the photons and the
> neutrinos and gamma rays hit helium atoms, the helium atoms split back
> into individual hydrogen atoms, and absorb some energy in the process.
> Again, no physical laws are broken, and time is moving forward.
>
> Now, back on earth, everything is playing out in reverse as well. You
> breath in carbon dioxide and absorb heat from your surroundings and
> use the heat to break the carbon dioxide into carbon and oxygen. You
> exhale the oxygen, and you turn the carbon into sugars, which you
> eventually return to your digestive track where it's reconstituted
> into food, which you regurgitate onto your fork and place it back onto
> your plate.
>
> Okay. So, still no physical laws broken. Entropy is decreasing, but
> that's not impossible, just very unlikely under normal conditions.
>
> Now. Your brain is also working backwards. But exactly backwards from
> before. Every thought that you had yesterday, you will have again
> tomorrow, in reverse. You will unthink it.
>
> My question is, what would you experience in this case? What would it
> be like to live in this universe where "external" time is still going
> forward, but where all particles are retracing their steps precisely?
>
> The laws of phsyics are still working exactly as before, but because
> all particle trajectories were perfectly reversed, everything is
> rolling back towards the big bang.
>
> In my opinion, we wouldn't notice any difference. We would not
> experience the universe moving in reverse, we would still experience
> it moving forward exactly as we do now...we would still see the
> universe as expanding even though it was contracting, we would still
> see the sun giving off light and energy even though it was absorbing
> both. In other words, we would still see a universe with increasing
> entropy even though we actually would live in a universe with
> decreasing entropy.
>
> And why would that be the case? Because our mental states determine
> what is the past for us and what is the future. There is no "external
> arrow of time". The arrow of time is internal. The past is the past
> because we remember it and because the neurons of our brains tell us
> that it has already happened to us. The future is the future because
> it's unknown, and because the neurons of our brains tell us that it
> will happen to us soon.
>
> If there is an external arrow of time, it is irrelevant, because as
> this thought experiment shows it doesn't affect the way we perceive
> time. Our internal mental state at any given instant determines what
> is the future and what is the past for us.
>
I was with you up to that last sentence. Forward or backward, we just
experience increasing entropy as increasing time, but that doesn't
warrant the conclusion that no process is required and an "instant"
within itself has an arrow of time.
> In fact, you could run the universe forwards and backwards as many
> times as you wanted like this. We would never notice anything. We
> would always percieve increasing entropy. For us, time would always
> move forward, never backwards.
>
> My point being, as always, that our experience of reality is always
> entirely dependent on our brain state. We can't know anything about
> the universe that is not represented in the information of our brain
> state at any given instant.
>
> Forwards or backwards, it's all just particles moving around, assuming
> various configurations, some of which give rise to consciousness.
>
> Again, assuming that there actually is an external physical world. We
> could, I think, apply the same idea to running a computer simulation
> of a human brain in reverse where instead of computing the next state,
> we compute the previous state.
That was my point in asking Bruno whether there is a universal
reversible computer (Turing machines obviously aren't reversible).
Since a QM (without collapse) model of the universe is reversible,
absent a reversible computer either the universe could not be computed
or QM is wrong.
Brent
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Received on Wed Apr 22 2009 - 11:02:16 PDT